The invention relates to a method for controlling reeling in the reel-up of a web. The invention also relates to an apparatus for controlling reeling in the reel-up of a web.
The reel-ups of web-like materials are used for reeling a material passed as a continuous web into a tight reel, so that it can be transferred to further processing. For example in reel-ups of a paper web, a continuous paper web passed from a paper machine, coating machine or a corresponding paper processing apparatus is wound around a reel spool to form a reel. The web is brought onto the reel via a reeling cylinder which is arranged rotatable and against which the reel is pressed by means of a loading device provided in connection with the reel spool. Thus, the web enters the reel so that it is pressed in between the preceding layers of the reel and the mantle surface of the reeling cylinder. At this point, where the web enters in contact with the preceding layers of the reel, the web is subjected to a particular nip load, linear pressure, produced by the aforementioned loading device. In current reel-up types, the reel spool is also centre-driven, and by means of the torque of the reel spool it is also possible to affect the peripherical force of the web to be reeled.
The reeling nip between the reeling cylinder and the reel is primarily used to prevent air from entering the reel. By controlling the load applied to the web, it is, however, also possible to control the tightness of the roll that is building, and furthermore, the aim is to change the load during the reeling so that at different points of the radius of the reel, the tightness of the reel would correspond to the quality requirements set in accordance with the paper grade and after-treatment of the reel. The properties correlating with the tightness of the reel include reel hardness and reel density.
Methods for affecting the web in order to attain a suitable hardness or density distribution in the direction of the radius of the reel, are described for example in the Finnish patent 71107 in which the reel spool rests on supporting rails and is loaded towards the reeling cylinder, and this loading force is adjusted in such a way that the loading force is reduced e.g. in accordance with a predetermined loading program as the radius of the reel grows. When adjusting the loading force, one has to take into account the geometry of the loading mechanism, which requires a separate sensor application therein so that it is possible to make the necessary corrections when reducing the loading force. Moreover, other disturbing factors of the loading mechanism and the loading device which affect the actual load of the web, are disregarded.
Furthermore, the Finnish public patent application 884651 discloses a method in which the mass of the web reeled around the reel spool is continuously calculated so that it would be possible to take into account the effect of the weight of the reel when the reel is placed against the reeling cylinder before moving onto,the supporting rails where most of the reel is formed.
The purpose of the invention is to present a method of a new kind for controlling the reeling process during the entire process of reel formation. The purpose of the method is to eliminate the disturbance factors due to the mechanics, as well as other external disturbances, and to enable the reeling in such a way that each paper grade is provided with the correct density in different parts of the reel.
The control of the reeling process utilizes the reel density as a measured variable determining the load to be applied to the web. The reel density of the formed reel can be determined by measurements and calculations conducted with suitable sensors, either continuously or at sufficient frequent intervals.
Because the measured variable used is the reel density, i.e. the variable which is the final objective of the reeling process, it is possible to determine for each paper grade e.g. an optimal density curve, or, with respect to different purposes, optimal density curves as a function of the size (diameter or radius) of the reel. During the reeling process, this curve can be achieved as accurately as possible by taking the reel density corresponding to each momentary size of the reel as a set value and by changing the load applied to the web in such a way that this set value is attained.
Furthermore, the purpose of the invention is to present an apparatus for controlling the reeling process, by means of which the apparatus the aforementioned objectives to produce a reel with the desired density distribution are achieved. The apparatus constitutes a closed loop which comprises a calculating unit for calculating the reel density according to the measurement values issued by from a sensor, and a comparator and control unit for comparing the value with the set value and for adjusting the manipulated variables affecting the density on the basis of the information.